You don't need to cap. If you hover over the little fireball-like symbol just to the right of "Weekly Sun Scrolls" at the bottom of your Daily Practice page, it'll tell you how many you need. Assuming it's constant across all characters & servers, that's 5,000 sun scrolls to activate the bonus out of a potential 5,800. Moon Scrolls appears to be 40,000.

It's not about capping, it's about reaching the required amount. If you were already past that when the season started, you won't get credit. You can only complete those cherries twice this month, though, so missing it isn't significant. You've still got 4 more chances to get those 2 completions.